1. Technical Field
The present invention relates to a power supply apparatus for display monitors, and more particularly, relates to a power supply apparatus having a simplified power factor correction circuit incorporated therein for display monitors in computer systems.
2. Related Art
Generally, power supplies for display monitors such as cathode ray tube (CRT) monitors commonly used with computer systems are designed to provide the necessary voltages and currents within the desired specifications using internal control. A typical computer-controlled power supply for use in computer systems includes an AC line rectification, AC loop regulation and power factor correction as disclosed in U.S. Pat. No. 5,019,717 for Computer-Controlled Uninterruptable Power Supply issued to McCurry et al. Some power supply systems may include power saving circuitry to reduce power consumption such as disclosed in U.S. Pat. No. 5,335,168 for Computer System With Power-Down Mode For Monitor issued to Walker, U.S. Pat. No. 5,375,245 for Apparatus For Automatically Reducing The Power Consumption Of A CRT Computer Monitor issued to Solhjell et al., and U.S. Pat. No. 5,481,730 for Monitoring And Control Of Power Supply Functions Using A Microcontroller issued to Brown et al. Other designs may include special circuitry to eliminate interferences such as disclosed in U.S. Pat. No. 4,886,979 for Power Source Circuit Device For Monitors And Host Computers issued to Chang, and hazard prevention circuitry to prevent hardware power failure such as disclosed in U.S. Pat. No. 5,481,732 for CRT Monitor Power Control Circuit issued to Shahbazi.
Typically, the power supply system is provided with a power-off circuit for interrupting the electrical power supply to the monitor during a power off. In many systems however, power regulation need to be improved because the output power voltage fluctuates as a function of input voltage as well as a load variation. Moreover, additional display power management signaling control circuit is necessarily required to support the power factor correction. Accordingly, further improvement in the power supply circuit design can be contemplated.